The present invention relates to vehicle chargers, and particularly to an automatic detecting and switching vehicle charger.
Referring to FIG. 1, a prior art emergency device 1 of a charger of a vehicle is illustrated. In this prior art, battery 11 is connected to a positive electrode clip A and a negative electrode clip B (referring to FIG. 1xe2x80x941). The connecting ends A1 and B1 of the clips A and B, respectively, clamp the positive electrode C1 and negative electrode C2 of a car so that when the power of the vehicle is insufficient. The power can be conducted from the battery 11.
However, in general, when the emergency device 1 is actuated, since the two ends of the clips A and B are opened. If the two ends A1 and B1 are contacted to one another, a large short circuit will be induced so as to generate a spark. This will induce a great threat to the children. Moreover, it is possible that the two electrodes are connected reversely so as to destroy the devices in the vehicle, such as computers, audios, etc.
To improve this defect, in one design, a positive electrode voltage detecting circuit and a negative electrode voltage detecting circuit are used to detect the polarities of the charger C. Thereby, before conduction, the clips A and B are insulated, when the positive electrode voltage detecting circuit detects a positive voltage, the small power relay conducts, and meanwhile a large power relay will excite so as to form a loop.
However, above mentioned device has some defects. Firstly, when the clips A and B are connected with wrong polarities. Since the large power relay is conductive, the polarities cannot be determined correctly and thus short circuit cannot be effectively avoided. Moreover, since in general, the voltage of a vehicle charger is generally 12V or 24V, but it is often that the voltage of the charger is not clearly indicted, if the large power relay is connected. It is possibly that the battery will be destroyed. Thereby, the prior art charger protection device has still some defects.
Thereby, the object of the present invention is to provide an automatic detecting and switching vehicle charger; a power supply control circuit being connected to a positive electrode clip and a negative electrode clip for supplying power to a battery of a car; a conductive end of the positive electrode clip being further connected to an input end of the power supply control circuit through a signal conductive wire; the power supply control circuit comprising: a power supply unit including a first battery and a second battery, and a main switch for controlling the switching of power; a parallel connected relay unit including a small power parallel connected relay set which is formed by two parallel connected small power relays, and a large power parallel connected relay set which is formed by two parallel connected large power relays; a serial connected relay unit being formed by a small power serial connected relay set having a small power relay and a large power serial connected relay set having the large power relay; a low level positive voltage detection unit is a detection circuit which includes an operation integrated circuit, a resistor and a first transistor and an input point of the power supply control circuit being connected to a positive voltage through a diode in a positive direction for rising the voltage to a third pin of an integrated circuit; a high level positive voltage detecting unit including a comparator which is formed by an operation integrated circuit, a limiting resistor and a second integrated circuit; the high level positive voltage detecting unit being connected to the input end of the power supply control circuit through a diode along a positive direction; then input voltage being divided by the resistors and then the divided voltages are outputted to a fifth pin of the operation integrated circuit; a reference voltage unit being connected to input ends of the low level positive voltage detecting unit and the high level positive voltage detecting unit for providing reference voltage; a fault detection unit including an operation integrated circuit; an input end of the fault detection unit being connected to a lower level voltage of the reference voltage unit and an input end for detecting the fault of the input end; an alert unit being connected to an output end of the fault detection unit for alerting faults; a state display unit being formed by resistors and displays for displaying various conditions; the states are switched by a third transistor, a fourth transistor and diodes and resistor.
By above structure, when the main switch is actuated, if it is not conducted, the large power relays will not conduct so that the power supply unit and output end has no voltage; thereby, the object of short circuit proof is achieved; if the polarities of the power supply control circuit is connected, the input end will has a positive voltage; when the positive voltage is larger than the reference voltage of the reference voltage unit, the exciting coil of the small power relay will is excited and the exciting coil of the large power relay is induced so that a lower level loop is formed; if the positive voltage captured from the input end is divided and the divided voltage is larger than a reference voltage of the reference voltage unit, the third transistor will ground and conduct, then the small power relay will conduct so that the large power relay is excited; then, the two batteries are serially connected so as to form a high level conductive loop so as to trigger the fourth transistor to conduct so that the low level positive voltage detection unit is shorted to the negative electrode so as to cut off the circuit; if another clip is pulled out, if no voltage is derived from the input end, then the small power relay will stop exciting so that the power supply unit will turn off.